A. Field of the Invention
This invention relates to telephony communications and related telephone bus protocols.
B. Related Art
A digital telephone may conventionally include at least two types of ports: a telephone line interface for connection with a telephone network, and a data communications interface for communications with a computer. For example, the ROLMphone (R) 244PC includes a telephony port for providing connection to a telephone network switch, such as a private branch exchange (PBX), and two data communications ports for providing connection to a computer.
In conventional telephones, the telephony communications link may be provided using a variety of protocols. For example, in the 244PC the connection to the network switch is accomplished by way of ROLMlink protocol. In many other conventional telephones, the connection to the switch is established by using an industry standard protocol such as ISDN. Transfers on the link from the switch to the phone are said to be "downlink" while transfers from the phone to the switch are said to be "uplink".
Once the information arrives at the telephone, it is distributed to the telephone's various components by way of an internal bus. Conventionally, the telephony link is connected to the internal bus by way of a link interface, which translates the telephony information into the proper format and timing in accordance with the internal bus standard.
The internal bus may be one of a number of types. A conventional standard for such internal busses is General Circuit Interface (GCI). The GCI standard, describes, among other things, the structure of data frames and the timing of certain signals.
It is known in the art to have option cards or modules which plug into the telephone's internal bus. For example, a plug in option card may be used to provide the telephone with a data connectivity feature. Sometimes, a dedicated slot or bay will be provided for each option, thus enabling the telephone to easily recognize which options are present or absent. In other instances, the options are connected to a common parallel bus having one conductor for each telephone signal or control line of interest.